Zero waste processing of wastewater sludge – production of biocoke

Summary

Municipal wastewater sludge has been dominant anthropogenic waste. The problem of its utilization is typical for any city operating a modern system of wastewater treatment. The tasks of optimal sludge utilization have not been solved on the global scale so far. In European practice different, often non-optimal technical solutions depending on the severity of the national environmental standards are applied. In a number of European countries expensive sludge incinerators have been built that provide for thermal utilization of the bulk sludge volume. The generated energy is used in the central heating systems. This technology is considered the most advanced though up to now it has not been supplemented with a cost-efficient and environmentally substantiated technology of processing generated ash. In Russia the bulk of sludge is landfilled; however, the need of developing efficient and environmentally acceptable technology of sludge utilization has become imminent. Pyrolysis is a possible solution of low waste sludge processing with conversion into a useful product – biocoke. The technologies of pyrolysis organic waste processing have a number of advantages over incineration.

Zero waste processing of wastewater sludge – production of biocoke

Summary

An optimal method of wastewater sludge utilization has not been found so far. An advantageous method of wastewater sludge utilization (both economically and ecologically) can be production of biocoke – material that meets the following criteria: high concentration of pure carbon (more than 15–30%); low hydrogen concentration (H/C less than 0.2); the lack of organic toxicants; high porosity (about 40%); mechanical stability; good sorption properties. Method of production – pyrolysis at 400–900 °С temperature; raw material – organic wastes of different origin (wastewater sludge, agricultural wastes, milling wastes, poultry farm wastes). Biocoke can be used for soil conditioning, reclamation of solid waste landfills, reclamation of technogenic and abandoned territories for planting, mitigation of land erosion and desertization. Compared to other soil media biocoke has an advantage in the possibility of selecting material properties depending on the specific application. AktivIl Company has designed and commissioned a medium-scale multiple-hearth pyrolysis reactor with a capacity of approximately 300 tons of biocoke annually; sludge from a wastewater treatment plant in one of the Moscow Area cities has been used as a raw material. Biocoke samples produced at different operating modes were analyzed and tested. The first results of the studies showed the possibility of reaching the required parameters of the product. The studies are going on within the frames of some national and international projects.